Electrothermal guns that use inert, safe-to-handle, propellants have been contemplated. See for example, U.S. Pat. Nos. 5,549,046; 5,072,647; 5,012,719; 4,974,487, the disclosures of which are incorporated herein by reference, which describe the use of a high pressure gas pulse to propel a projectile or projectiles out of a gun barrel. A source of gas is obtained by combusting an inert safe-to-handle propellant. The propellant is typically composed of a fuel, namely a metal hydride or metal, such as aluminum powder, and an oxidizer, namely water or a water-hydrogen peroxide mixture. Combusting a slurry of metal powder and water in a closed chamber generates high pressure gas, namely hydrogen gas, and a metal oxide aerosol. The apparatus and method for combusting such a propellant is well known, namely applying a high pulsed voltage through an electrode to produce an electrical discharge or plasma, which changes water to steam and vaporizes the metal powder in an exothermic chemical reaction, forming hydrogen gas and metal oxide particles aerosol.
Inert propellants are highly desirable since they are difficult to combust, making them safer to manufacture and handle. While the hydrogen gas component is useful for propelling a projectile or projectiles out of a barrel, the metal oxide aerosol component is undesirable, due to a tendency of the metal oxide aerosol to erode the barrel of the gun and to decrease the overall efficiency of the process. Accordingly, it would be desirable to provide a mechanism for separating the metal oxide aerosol component from the hydrogen gas component that results upon combustion of the propellant. Separation of the two combustion components would result in increased barrel life and an increase in the overall efficiency of the combustion process.